An increasing number of recent tumor growth studies have focused on inhibition of angiogenesis as a means of preventing tumor metastasis. As a result, several anti-angiogenic agents have been described, including placental ribonuclease inhibitor. Preliminary research completed by Promega Corporation in collaboration with the University of Wisconsin has indicated that an endotoxin-free form of recombinant ribonuclease inhibitor -- RNasin ribonuclease inhibitor -- may have the ability to prevent tumor growth. The ultimate goal of this research is to confirm the potential efficacy of RNasin ribonuclease inhibitor as an anti-cancer drug, capable of inhibiting tumor growth. To determine the feasibility of attaining this goal, Phase I studies will focus on: 1) demonstrating that RNasin inhibitor can a) be prepared in a form suitable for animals, and b) inhibit angiogenesis; 2) determining stability of RNasin inhibitor under test conditions, and 3) determining dosage and time of treatment to reduce angiogenesis associated with tumor growth. Phase II will focus on a) increasing the anti-angiogenic activity and systemic retention of RNasin inhibitor, b) broadening examination of anti- angiogenic activity, c) confirming RNasin inhibitor's efficacy in reducing tumor-associated angiogenesis and growth, and d) determining the mechanism by which RNasin inhibitor reduces angiogenesis.